Mass spectrometry is a powerful tool for identifying a molecule or ion by its mass-to-charge ratio. A limitation of mass spectrometry is the difficulty of rapidly measuring biomolecules or macromolecules of high mass-to-charge ratio. Recent advances in the detection of large biomolecules include matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI).
Mass spectrometry has been applied to the study of proteins, organelles, and cells to characterize molecular weight, as well as to study products of protein digestion, proteomic analysis, metabolomics, and peptide sequencing, among other things. Ion trapping devices and methods such as three-dimensional quadrupole ion traps have been useful for proteomics in general because they provide mass-selective ejection of ions from the trap.
In brief, mass-selective ejection of ions from a trap can be done by frequency-scanning a resonant LC circuit of the mass spectrometer in which the ion trap is the capacitor. The frequency sweep can be made to correspond to a range of mass to charge ratios for the detected ions.
A drawback of mass-selective ejection of ions from a trap by frequency-scanning methods is that when sweeping over a frequency range, no specific frequency is completed over an entire cycle before changing to the next frequency. Moreover, each successive frequency in the sweep begins at an arbitrary phase. These drawbacks reduce the resolution of the mass spectrum and the correspondence of the frequency to the mass to charge ratio.
There is a continuing need for methods for detecting proteins and biomolecules using a mass spectrometer. There is also a need for an apparatus and arrangement for a mass spectrometer that can detect large biomolecular ions. There is a further need for a mass spectrometer apparatus and methods capable of detecting biomolecules rapidly at high resolution for studies in proteomics.